Dual-lenticular-lens-based 2-D/3-D convertible autostereoscopic display Nobuaki Takanashi Shin-ichi Uehara Jyun-ichiro Ishii Hiroshi Hayana Hideki Asada Abstract — A 2-D/3-D convertible display using two lenticular lenses has been developed. It shows 2-D pictures in full resolution and 3-D autostereoscopic pictures in half resolution by moving one lens relative to the other. The lens assembly consists of thin metal frames, two lenticular lenses, and two shape-memory-alloy (SMA) wires used as actuators. While this assembly is applicable to flat-panel displays of any kind, its simple structure and low power consumption make it best suited to mobile terminals, such as PDAs and mobile phones. Here, we describe its structure and present evaluation results. Keywords — 3-D, flat-panel display, lenticular lens, actuators. 1 Introduction Many 3-D display systems have been developed for enter- tainment, medical, design, and other applications. They are expected to appear in mobile terminals soon. One key to a mobile 3-D display is the so-called autostereoscopic display, which does not require the viewer to wear any special glasses for 3-D viewing. For this type of 3-D display, tracking the user’s viewpoint is important. Hamagishi et al. have developed a desktop autostereoscopic display with a moving a liquid-crystal (LC) image splitter. 1 Their system measures the user’s head with a camera and adjusts the 3-D viewing area by moving the LC image split- ter. However, this structure is complex. In mobile applica- tions, the user adjusts his viewing position himself, so no tracking mechanism is needed. Thus, a simple 3-D display can be used for mobile applications. Another key for a mobile 3-D display is the ability to convert between a 3-D display and a full-resolution 2-D dis- play. Because the main applications on mobile terminals consist of viewing 2-D contents, full resolution is needed to view fine 2-D contents, while two images (in half resolution) are needed to view 3-D content. This convertibility require- ment distinguishes mobile applications from the 3-D sys- tems used for entertainment on big screens. To achieve 2-D/3-D convertibility, Harrold et al. have developed a “latent” parallax barrier autostereoscopic dis- play. 2 Their display has a retarder array which has slit and non-slit regions with different polarizations. The display switches between the 3-D and 2-D modes when an addi- tional polarizer is placed on or removed from the LCD. Ishii et al. have developed a lenticular-lens-based 2-D/3-D convertible autostereoscopic display. Their display achieves the convertibility by floating a lenticular lens over the LCD. 3 When the lenticular lens is placed on the LCD, adjoining pixels are viewed by the right and left eyes sepa- rately. When the lens is floated away from the LCD, its func- tion disappears and all pixels are viewed in full resolution as a 2-D display. Although both types of these systems achieve 2-D/3-D convertibility, the parallax-barrier-based system is inferior with respect to brightness and 3-D stereo image separation. On the other hand, although the lenticular-lens-based 3-D display is brighter than the barrier-based one, the floating structure needs extra space above the LCD. To resolve this problem, we propose a novel dual-lenticular-lens structure. This architecture achieves 2-D/3-D convertibility by sliding two lenticular lenses relative to each other. The structure is thin and simple, because of its sliding-motion design and the use of shape-memory-alloy (SMA) as actuators. We also developed an evaluation system to measure the display per- formance with this structure. This paper describes the basic structure and presents evaluation results. 2 Principle and optical simulation Figure 1 shows the principle of the dual-lens autostereo- scopic display. Two lenticular-lens arrays, each having a two- pixel-wide lens pitch, are set facing each other. In 3-D mode, the two arrays are placed so that the lens tops meet and the whole lens assembly acts as a single lenticular-lens array. The lenticular lens causes the observer to view two adjacent pixels on the display separately with his left and right eyes. In 2-D mode, the two lenticular-lens arrays are placed so that one is shifted by half the lens pitch relative to the other. In this configuration, the functions of the lenticu- lar lenses cancel each other out and produce no overall lensing effect, so two adjoining pixels on the display are viewed by both eyes simultaneously. One merit of the proposed structure for mobile termi- nals is its thinness. Because the motion for switching modes Revised version of a paper presented at the Twenty Third International Display Research Conference (IDRC ‘03) held September 16–18, 2003, in Phoneix, Arizona, U.S.A. The authors are with SOG Research Laboratories, NEC Corp., 1120 Shimokuzawa, Sagamihara, Kanagawa 229-1198, Japan; telephone +81-42-771-0689, fax -0780, e-mail: n-takanashi@ay.jp.nec.com © Copyright 2004 Society for Information Display 1071-0922/04/1203-0335$1.00 Journal of the SID 12/3, 2004 335